Jun 10 2010
If there’s one thing the media love, it’s a “bungling bureaucrats” story. Yep, the FDA, wrapped up with their science dogma, enslaved to Big Pharma, pushing toxic, unnatural chemicals and ignoring safety data. And that’s the story being told about sunscreens:
What’s a consumer to do? If you only read the headlines, you may get the impression that sunscreens do more harm than good. The impetus was the release of the Environmental Working Group’s (EWG) 2010 Sunscreen Guide. EWG is an environmental advocacy organization that focuses on consumer products, and has been conducting annual reviews of sunscreens since 2007. Of the 500 products it reviewed, it only recommends 8%, or 39 products in total. Why were so many products deemed “not recommended”? Reasons for negative ratings included the following:
- any product containing retinyl palmitate (vitamin A), which is described as a photocarcinogen
- any product containing oxybenzone, called a “potential hormone disrupter”
- any sunscreen packaged as a spray or powder, due to inhalation concerns
EWG also raised concerns about nano-sized particles in sunscreens. But before we dive into the report, let’s consider what we’re trying to do with sunscreen.
Effects of UV Radiation
Ultraviolet radiation that reaches the earth may be divided into UVA (320–400 nm) and UVB (290–320 nm). UVA is further subdivided into UVA I, II and III. A simplified way to differentiate between the two types is to think of UVA as the aging radiation, and UVB as the burning radiation. Your exposure to UV radiation depends on factors such as latitude, altitude, time of year/day, and atmospheric conditions such as clouds and pollution. For example, if you’re on the Mediterranean coast at noon in the summer, the radiation mix is about 95% UVA, and 5% UVB.
UVB has been the traditional focus — stop the sunburn. UVA wasn’t scrutinized. But not only can UVA pass through glass, its rays can penetrate deeper into the skin and are responsible for skin breakdown and thickening. Both UVA and UVB are now implicated as cancer-causing, and UV radiation is considered a carcinogen.
Acutely, we see the effects of UVB. Sunburns can range from mild redness to life-threatening situations. Long term, the skin will show signs of both UVA and UVB damage. Degenerative changes including skin thickening as well as fibrous tissue and circulatory changes follow chronic exposure. And then there’s the big worry: cancer.
Why use Sunscreen?
Sunscreens reduce UV damage by reflecting or absorbing UV radiation:
- Physical (inorganic) barriers (i.e., zinc oxide and titanium dioxide) physically block the skin from sunlight with particulate matter, reflecting and scattering UV rays. Physical barriers are near-perfect sunscreens: they protect against UVA and UVB, they start working immediately, they’re stable and don’t break down in the sun, and they are safe. Their use has traditionally been limited by aesthetic qualities, with formulas that are greasy, white, and opaque.
- Chemical (organic) barriers filter and absorb UV radiation. Their chemical structure converts UV radiation to heat. They vary in their chemical properties, as well as their ability to absorb UVA, UVB, or both.
The Sun Protection Factor (SPF) is a estimate of how effectively a sunscreen will reduce the time to a sunburn. For example, a sunscreen that extends burning time from 10 minutes to 150 minutes has an SPF of 15. Because sunburn is the endpoint measured, SPF is a measure of UVB protection, not UVA protection. While UVA is implicated as a carcinogen, along with UVB, there are currently no well-established short-term endpoints for measuring UVA protection. But this is changing, with the FDA proposing a new set of rules for labeling UVA protection.
There is little difference in sunscreens beyond SPF 15. Consider the following:
- SPF 15 will allow 7% of UVB radiation through to the skin
- SPF 30 will allow 4% of UVB radiation through to the skin
- SPF 60 will allow 2% of UVB radiation through to the skin
SPF values are calculated based on a dose of about 1oz (30mL, or 2 tablespoons) for the entire body — much more than is typically used. In general, insufficient amounts of sunscreen are applied to achieve the labeled UV protection. In real-world observations of use, actual protection is limited far more by the amount applied, and how often it is reapplied, than by the SPF. The EWG report illustrates the consequences of inadequate use of sunscreens, based on applying one-quarter of the recommended amount:
|SPF on label||Average SPF of users at(0.5 mg/cm2)||% UV transmission (amount reaching skin)|
When used properly, SPF 15 provides more than adequate UVB protection for most individuals. EWG recommends that higher SPF products should be avoided if they contain higher concentrations of ingredients they deem potentially hazardous. While it’s unclear how much risk these ingredients truly represent, it’s a fair statement that higher SPF products are more about marketing, rather than meaningful differences in potential sun protection. You get better protection using a sunscreen properly.
Sunscreens and Cancer
There are three major types of skin cancer. Basal cell carcinoma and squamous cell carcinoma are common, but rarely fatal. They often appear on sun-exposed areas like faces and ears, and can be removed easily (though it may be disfiguring). It’s clear that sun exposure is a risk factor for basal cell carcinoma and squamous cell carcinoma, and that sun avoidance can reduce this risk. The third cancer, melanoma, is rare (about 3% of all skin cancers) but frequently fatal, causing 75% of the deaths). When it comes to melanoma, the data on sun exposure are not as clear. There isn’t good evidence to demonstrate that reducing sun exposure has an effect, as chronic sun exposure seems to have a protective effect. However, there is good evidence linking sunburns, and particularly intermittent sun exposure to melanoma. The data with indoor tanning also seem to support a dose-response relationship. Overall, the data points to an association between intentional sun exposure and melanoma, non-intentional sun exposure with squamous cell carcinoma, and basal cell carcinoma likely related to both. (Source)
When it comes to the efficacy of sunscreen to reduce cancer risk, the data are less clear. Most sunscreens didn’t offer UVA protection until recently, confounding studies examining relationships between sunscreen use and cancer risk. Consequently, the evidence linking sunscreen use to reduced melanoma risk isn’t convincing. Studies are confounded by the long latency period for melanoma, the challenges with recall studies, and the changing formulations of sunscreens. One hypothesis for the lack of link is that sunscreen could confers a false sense of security, increasing overall exposure through more time in the sun, and possibly less use of protective clothing. Compounding this would be a relative lack of protection against UVA. Overall, however, there’s good evidence to demonstrate sunscreen use can reduce precursors to cancer, and the incidence of squamous cell cancer. On balance, the data suggest that sunscreens provide protective effects against cancer.
Pharmaceutical Elegance: The Importance of Formulation
One consideration I frequently discuss when counseling consumers about sunscreens are questions and concerns about aesthetics — particularly in products for children. If the product is greasy, opaque, or thick, it won’t be used properly, no matter how effective the product might be. Aesthetics are a function of the vehicle (what the active ingredients are mixed in) as well as the specific characteristics of the compound. Alcohol-based and “dry” versions are also available, but must rely on a smaller number of ingredients because of manufacturing issues.
A related problem is photostability — the ability of sunscreens to remain effective when irradiated by UV rays. Photostability is a function of the vehicle, and the type and concentrations of the different ingredients. Inorganic sunscreens don’t have this problem: not only are they photostable, they are also ideal for those with sensitive skin that may be allergic to organic chemicals.
In general, if the final product doesn’t have great aesthetics, it probably won’t be used properly. And this compromises the point of using sunscreens in the first place.
Acute side effects of sunscreens are rare and are generally limited to hypersensitivity reactions, such as skin rashes to the chemical (organic) sunscreens. Longer term effects can be categorized into two categories: long term toxicities from the constituents of the sunscreen (the bulk of the Environmental Working Groups’s concerns) and the potential for reduced vitamin D absorption.
While vitamin D production is blocked when UVB-blocking sunscreens are used, the real-world impact isn’t clear. Deficiency is plausible, but there’s little evidence to suggest meaningful deficiencies in vitamin D are related to typical use of sunscreens.
Is Retinyl Palmitate Causing Cancer?
The EWG report evaluates the different ingredients and formulations of sunscreens and uses its own ranking system to assign a score. Their scoring system is internally developed, and has not been validated, but the methodology is reasonably transparent.
Based on the coverage of the EWG’s report, you might get the impression that sunscreens containing retinyl palmitate are causing cancer. Retinyl palmitate is a form of vitamin A commonly used in cosmetic products to reduce wrinkles and fine lines. The EWG points to a 2009 study of retinyl palmitate on mice as their main cause for concern. Treated mice, and a control group were exposed to the equivalent of nine minutes of noontime Florida sun daily, for a year. Compared to the control group, the RP group developed more tumours. That’s adequate evidence to avoid the product says the EWG. But is this finding relevant? The mice were treated with retinyl palmitate — not sunscreen that contained retinyl palmitate. It’s known that retinyl palmitate can be a photosensitizer. When used as a single ingredient cream, as with other forms of vitamin A, you must wear sunscreen, or you’ll burn more easily. So how relevant is this mouse study to human subjects, wearing sunscreens containing retinyl palmitate? It’s difficult to say. Study completion and peer review is expected by 2011. What’s the best approach until then? Well, given that retinyl palmitate isn’t approved as a sunscreen, there’s no compelling rationale for it to be in these products. It’s not unreasonable to avoid it if desired, but there’s no persuasive evidence to suggest its presence is a sound reason to skip sunscreen.
Oxybenzone: Disrupting our Hormones?
Oxybenzone, or more properly, 2-hydroxy-4-methoxybenzophenone, is naturally found in flower pigments and is commercially synthesized as a sunscreen agent and UV stabilizer. Oxybenzone provides UVB and some UVA protection, and stabilizes avobenzone, an effective (but less chemically stable) UVA-sunscreen agent. It has been the target of criticism by those asking for more long-term safety assurances. The CDC recently reported that oxybenzone was detected in 97% of urine samples in a representative sampling of Americans. So it’s in our bodies and in our environment. Is it harmful?
EWG says yes, calling it a “potential hormone disrupter”. Yet oxybenzone hasn’t been linked conclusively to negative health effects. But absence of evidence isn’t evidence of absence, so do consumers have cause for concern? The CDC notes, “Human health effects from benzophenone-3 at low environmental doses or at biomonitored levels from low environmental exposures are unknown.” The European Union’s review is online [PDF], which asks for more information on dermal absorption, yet concludes that in vitro and in vivo data indicate oxybenzone does not possess photo-mutagenic or photo-genotoxic properties.
EWG recommends that oxybenzone should be avoided in sunscreens. However, evidence isn’t yet persuasive that meaningful hazards have been documented. It’s important to recognize that EWG takes a strict perspective on ingredients that is not shared by other organizations. Because something is in the environment at very low doses, it does not mean it is harmful. In addition, the ubiquity of oxybenzone in personal care products makes it very difficult to avoid, as the CDC sampling showed. As the American Cancer Society points out in its discussion of cosmetics,
It’s important to have a sense of the difference between the hazard an ingredient may pose and the risk a person faces from being exposed to it. Scientists use the term hazard to describe the potential of a chemical to cause unwanted health effects. Risk is used to describe the chances of an unwanted health effect in a person from normal use of the ingredient. A substance may be deemed to be potentially hazardous for some reason, but it may pose very little risk to people during normal use.
When it comes to oxybenzone and sunscreens, the myriad of alternatives available mean that it’s possible to avoid oxybenzone if desired, while still finding products that provide good UV protection.
If we want to avoid organic (chemical) sunscreens, the inorganic options, titanium and zinc are the attractive alternative. But EWG raises further concerns about new formulations of these products — those that contain nanoparticles. Nanoparticles are a new innovation to deal with the aesthetic drawbacks of the physical sunblocks: Make the particles small enough, and they become translucent and even transparent. Traditional titanium dioxide and zinc oxide have particle sizes of over 200 nm — large enough to reflect visible light, giving the traditional white appearance. Make the particles small enough, and they won’t scatter visible light. (This chart [pdf] nicely illustrates the effect.) EWG is concerned about the risk of absorption of nano-particles and is calling for more research. However, they note the following:
Although we expected to reach a different conclusion at the outset of our sunscreen investigation, when we balanced all factors important in sunscreen safety, our analysis shows that many zinc and titanium-based sunscreens are among the safest and most effective sunscreens on the market.
This statement is evidence-based. Measurable systemic absorption does not seem to occur with titanium and zinc nano-material sunscreens. EWG does flag sprays and powder forms of sunscreens as potentially problematic, particularly the nano-formulations, due to inhalation risks of sunscreen ingredients. While the risk of absorption is certainly greater with aerosols, compared with creams, this can be mitigated by selecting liquid sprays instead of dry powders, and avoiding spraying directly on the facial area. Probably the biggest drawback to nanomaterials is that as the particles get smaller, the UVA protection diminishes. Consequently, ultrafine particles may need to be combined with chemical sunscreens to provide complete (broad spectrum) protection. On balance, the inorganic sunscreens, whether they are nano-sized or not, are excellent sunscreens.
Sunscreen is not a panacea for skin protection. Sun avoidance and physical barriers remain the best approaches to minimizing the acute and long-term effects of UV radiation. The data on sunscreen use and cancer risk are complex, but on balance suggest that the short-term and long-terms benefits of sunscreens significantly outweigh their risks when used during periods of unavoidable exposure. There’s no evidence that vitamin D deficiency is a consequence of safe sun behaviours, and given there are safe and inexpensive methods of obtaining vitamin D (oral supplementation) the rationale for intentional, unprotected sun exposure remains unclear.
Sunscreens remain an important option to help avoid unwanted UV exposure. Overall, the EWG report makes it easy for consumers to differentiate between sunscreens, and make selections based on UV spectrum protection and ingredient preferences. While I’m personally not convinced about the hazards of the current FDA-approved products, I agree with the group’s overall recommendation that physical barriers, containing titanium and/or zinc, have superior risk/benefit profiles. When you look past the headlines, the Environmental Working Group’s analysis isn’t bad. It’s cautious but pragmatic. The bad probably isn’t as bad as they say, but they take a good perspective related to risk/benefit overall.
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